This invention relates to fluid selective control devices, and more particularly to arrangements for testing seals which isolate a controlled fluid from its environment. The invention is more specifically directed to devices in which a seal between two mating surfaces can be externally tested. Favorably, the invention concerns the seal formed between a filter and the supporting framework therefor, which is intended to prevent air from leaking through or bypassing the filter. In a specific environment, the invention is directed to an arrangement for testing the seal for a type of filter which removes particulates and other contaminants from the air flow into or through a clean room device, such as a clean room or a laminar flow bench. In this specification, the term "clean room device" shall mean, inclusively, a clean room, a cabinet, a laminar flow bench, or any similar instrument or device.
In the conventional sealing arrangement for High Efficiency Particulate Air (HEPA) filters or other clean room filters, a gasket is disposed between the filter frame and its associated seat or holder, forming a single annular seal. Generally, testing for leaking or bypassing involves an elaborate procedure, a typical example of which is described in U.S. Pat. No. 4,324,568. A disbursed particulate, such as DOP or the like, is injected into the air flow to determine if any particles are leaking around the filter material. This procedure requires a considerable investment in equipment, and is capable of detecting leaks only in the downflow direction and cannot test the integrity of the seal in the upflow direction.